What you did first can work if you do it right, but it gets confusing. It is better to recolour the tiles to fit the tileset first, as it is visibly easier to do, replace the tiles in the tileset with your new tiles and then pallette edit in Advance Map.
Nope, too busy. I wouldn't automatically give someone a tileset before they confirm, as that is assuming, and can annoy. Especially if the person's motto is "Never assume", like mine is.